In correspondence to recent tightening of exhaust restriction, improvement in accuracy of fuel injection control of an engine is required. From the viewpoint of securing a required engine performance, there is a serious problem that an injector has a variation in its precision of fuel injection amount according to a secular change thereof or because of precisional dispersion thereof when it is produced (hereinafter, the variation is referred to as Q-lag).
As trials for solving the problem of Q-lag, injectors are checked at the production thereof so as to reduce the precisional dispersion, or their quantities in injection or the like are checked. However, these trials are disadvantageous because of increasing production cost. These trials are also disadvantageous because the problem of Q-lag is not solved fundamentally.
As a fundamental means for solving the problem, it is conceivable to feed back a torque actually generated in the engine, that is, a fuel injection amount, so as to correct the Q-lag. For example, in the engine disclosed in the Japanese Patent Laid Open Gazette 2000-328999, the Q-lag is corrected based on engine output from a λ sensor.
However, since the λ sensor is provided in an exhaust system, response may be delayed in an engine having a supercharger or the like. As for an engine used in a car or a ship, the engine is often driven in a transient state, and the driving state of the engine in which the Q-lag is corrected is limited to its idling range and its low speed traveling range in which load is relatively small. Accordingly, the engine disclosed in the Japanese Patent Laid Open Gazette 2000-328999 is disadvantageous because its driving range subjected to improvement in reduction of dispersion of fuel injection amount is limited.